The hundred-headed dragon that guarded the golden apples of the Hesperides was Ladon.
Ladon is described as a serpent-like dragon coiled around the sacred apple tree in the Hesperides’ garden at the western edge of the mythic world. The apples belonged to Hera, who received them as a wedding gift, and the Hesperides nymphs tended the garden. In some accounts, Ladon himself guarded the tree; in others, the nymphs shared that role.
Ladon appears during Heracles’ eleventh labor. One version says Heracles kills the dragon with arrows, while another has him persuade Atlas to retrieve the apples while Heracles temporarily supports the sky. In the Argonautica, the Argonauts later hear the Hesperides mourning beside Ladon’s still-twitching body.
The number of heads varies across traditions, but Pseudo-Apollodorus specifically gives Ladon one hundred heads and many different voices. Ladon is often confused with the Hydra, which Heracles fights in Lerna, or with Cerberus, Hades’ multi-headed hound. Hyginus also associates Ladon with the constellation Draco.